The major purpose of this project is to characterize in greater detail the active transepithelial ion currents which we have discovered in the dorsal lingual epithelium of several mammalian species. These ion fluxes arise in response to a variety of taste stimuli. The study extensively employs two in vitro electrophysiological methods and in vivo neurophysiological recording of gustatory responses. The first in vitro method is a novel adaptation of the Ussing technique which we have used to prove that the dorsal surface of the canine tongue actively transports ions. The active transport system is stimulated by hyperosmotic NaC1, a property not found in any other known transporting epithelium. It also responds to sugars (including sucrose) with increased inward transepithelial current. The response to sugars can be eliminated by the Na-channel blocker amiloride as can most of the hyperosmotic NaC1 response. The change in transepithelial current occurs over the same concentration range as the canine response to various tastants, including HC1. These transport properties are sufficiently unique so as to suggest a direct or indirect role for the transepithelial current in gustatory transduction. In order to gain a better understanding of these stimulus induced currents and their relationship to lingual epithelial morphology, we have begun to map the shape of the electric field outside the contours of individual papilla, while the tissue is open or short-circuited using a vibrating probe electrode. These studies should allow us to differentiate the role of taste buds in determining field magnitude and direction in the face of various taste stimuli. The neurophysiological studies on the rat are designed to allow us to correlate transepithelial events with gustatory neural events. This is done in two ways: by doing parallel in vivo and in vitro experiments in the same animal, and by making simultaneous transepithelial and neural recordings, in situ. These studies should provide a far clearer picture of peripheral events in gustatory transduction than is currently available. They suggest for the first time an ionic basis for the gustatory transduction of nonelectrolyte sugars. These studies should also lead to a clearer understanding of the role of active and passive ion transport in taste, the effects of hormones, and various metabolic factors which may govern food preferences and intake.